Feedback control for microfluidic cartridges

ABSTRACT

A device for sensing fluid movement within a microfluidic channel which uses feedback to control its operation. The device measures electric parameters to interpret fluidic parameters such as flow speed, and the presence or absence of fluid within the channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims benefit from U.S. ProvisionalPatent Application Serial No. 60/213,865, filed Jun. 23, 2000, whichapplication is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to microscale devices forperforming analytical testing and, in particular, to a microfluidiccartridge which uses embedded electrodes for feedback control in theoperation of its device.

[0004] 2. Description of the Prior Art

[0005] Microfluidic devices have recently become popular for performinganalytical testing. Using tools developed by the semiconductor industryto miniaturize electronics, it has become possible to fabricateintricate fluid systems which can be inexpensively mass produced.Systems have been developed to perform a variety of analyticaltechniques for the acquisition of information for the medical field.

[0006] Microfluidic devices may be constructed in a multi-layerlaminated structure where each layer has channels and structuresfabricated from a laminate material to form microscale voids or channelswhere fluids flow. A microscale channel is generally defined as a fluidpassage which has at least one internal cross-sectional dimension thatis less than 500 μm and typically between about 0.1 μm and about 500 μm.The control and pumping of fluids through these channels is affected byeither external pressurized fluid forced into the laminate, or bystructures located within the laminate.

[0007] The use of electrodes within microfluidic channels for themanipulation of fluids has been practiced extensively in the prior art.U.S. Pat. No. 5,126,022 teaches a device for moving molecules by theapplication of a plurality of electrical fields by the use of aplurality of electrodes which were placed at regular intervals along agel-filled channel which produced traveling electrical waves propellingcharged particles through the medium within the channel for separationand resolution purposes.

[0008] U.S. Pat. No. 5,989,402 teaches an electrically controlledmicrofluidic system having an electrical interfere array with aplurality of electrode pins which are oriented for insertion into aplurality of ports. The electrode pins on each electrically coupled to aseparate electrical lead, which leads are connected to an electricalcontrol system which concomitantly delivers a voltage to each of theleads.

[0009] U.S. Pat. No. 6,007,690 is directed to a device for performingmicrochannel electrophoresis in capillaries, in which the mainelectrophoretic flow path has associated with it at least one pair ofelectrodes for applying an electric field to the medium present in theflow path, thus providing for precise movement of entities along theflow path.

[0010] U.S. Pat. No. 6,171,850 is directed to a device for performingtemperature controlled reactions and analyzes in microfluidic systems.Heat exchangers are fabricated from a material that is both thermallyand electrically conductive, so that they can function as both a heatexchanger and an electrode when placed into a fluid filled reservoir.

SUMMARY OF THE INVENTION

[0011] It is therefore an object of the present invention to provide adevice which uses feedback from a sensing means to control operation ofa microfluidic device.

[0012] It is a further object of the present invention to provide adevice which measures electric parameters to determine the presence orabsence of fluid in microfluidic channels.

[0013] It is a still further object of the present invention to providea device which uses electrodes within microfluidic channels to measureflow speed and wetout.

[0014] It is still a further object of the present invention to providea device which uses optical sensors located in proximity to microfluidicchannels to measure wetout.

[0015] These and other objects of the present invention will be morereadily apparent in the description and drawings that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a representation of a flow sensor according to thepresent invention used within a microfluidic channel;

[0017]FIG. 2 is an enlarged view of the sensor and sensor holder of theflow assembly shown in FIG. 1;

[0018]FIG. 3 is an exploded view of the sensor carrier device shown inFIG. 1;

[0019]FIG. 4 is an assembled view of the device shown in FIG. 3; and

[0020]FIG. 5 is a plan view of an optical sensor assembly according thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Referring now to FIG. 1, there is shown a fluid sensor assembly,generally indicated at 10, according to the present invention. Assembly10 uses a fluid sensor 12, which is located within a microfluidicchannel 14 to monitor the flow of fluids within channel 14. Fluid isprovided to channel 14 via a fluid driving and control means 16. Means16, which may contain a separate fluid supply or merely pump fluid fromanother circuit into channel 14, is coupled to channel 14 at a channelinlet 18. The opposite end of channel 14 comprises a channel outlet 20,which end may be coupled into additional microfluidic circuitry.

[0022] Sensor 12 is electrically coupled to driving and control means 16by a cable 22. Cable 22 provides electrical signals from sensor 12 tomeans 16 relative to fluid flow within channel 14 at the location wheresensor 12 is positioned. These signals from sensor 12 may be used bymeans 16 to measure specific electric parameters, such as conductivityor capacity across channel 14. In addition, these electric parameterscan be used to interpret fluidic parameters, such as flow speed, or thepresence or absence of fluid within channel 14.

[0023] Means 16 is capable of analyzing signals received from sensor 12,and adapting the flow within channel 14 in response to informationreceived from sensor 12 via cable 22. This use of feedback signals tocontrol the operation of assembly 10 may be implemented by a computer,programmable controller, or any other device well known to personsfamiliar with this art.

[0024] Fluid flow within channel 14 may be in the form of a liquid or agas, and sensor 12 may be located at any point within channel 14, or mayconsist of multiple sensors located at different regions of channel 14.Means 16 may detect a gradient between different regions of channel 14and react to the differences, such as differences in flow speed orconductivity. As means 16 analyzes the information returned from sensor12, it reacts to adjust the operation of fluid driving within channel14.

[0025] Sensor 12 may consist of a single electrode, a series ofelectrodes, an optical sensing device, or even a hot wire anemometercapable of monitoring temperature changes within the fluid flowingwithin channel 14. Many sensing devices capable of performing theseoperations are well known in the art.

[0026]FIG. 2 illustrates an embodiment of the sensor and sensor holderwhich may be used in conjunction with the present invention. A sensor 30is shown having a pair of electrodes 32, 34 embedded within the body ofsensor 30. Sensor 30 is adapted to be inserted into an opening 36 withina sensor holder 38. Opening 36 is sized such that sensor 30 slides intosaid opening from the rear and is prevented from sliding out of the topby extensions 38 a of holder 38.

[0027]FIG. 3 is an exploded view of a sensor for use in the presentinvention. Sensor carrier device, generally indicated at 50, consists ofan upper layer 52, a central layer 54, and a bottom layer 56. Upperlayer 52 includes a plurality of apertures 60, 62, 64. Aperture 64allows sensor 30 to monitor conditions within a microfluidic channel inwhich carrier device 50 is mounted, while apertures 62, 64 provideaccess for the cabling to operate fluid sensor assembly 10. Layer 54includes a cutout section 66 for accommodating sensor 30 within carrierdevice 50, while bottom layer 56 is used to hold sensor 30 in its properposition for operation. The assembled sensor carrier device 50 can beseen in FIG. 4.

[0028]FIG. 5 illustrates the use of an optical sensor to determine thewetout of a microfluidic channel. Light source 70 is positioned inoptical proximity to channel 71 such that it illuminates a portion ofchannel 71. As channel 71 is filled, meniscus 72 creates an opticallydetectable signal (e.g., absorption or light scattering), which ispicked up by detector 73. The detector signal is then fed back throughleads 74 into fluid driver 75 to control the flow.

[0029] While the present invention has been shown and described in termsof several preferred embodiments thereof, it will be understood thatthis invention is not limited to these particular embodiments and thatmany changes and modifications may be made without departing from thetrue spirit and scope of the invention as defined in the appendedclaims.

What is claimed is:
 1. A microfluidic device, comprising: a microfluidicchannel having an inlet and an outlet; means associated with saidchannel and located between said inlet and said outlet, for sensingfluid flow within said channel, and generating electrical signalscorresponding to fluidic properties of the fluid flow; and means,coupled to said sensing means, for controlling fluid flow through saidchannel as a result of information obtained from said electrical signalsfrom said sensing means.
 2. The device of claim 1, wherein said sensingmeans comprises an electrode assembly.
 3. The device of claim 2, whereinsaid electrode assembly includes a plurality of electrodes.
 4. Thedevice of claim 1, wherein said sensing means is positioned within saidmicrofluidic channel.
 5. The device of claim 1, wherein said controlmeans further comprises: means for analyzing said electrical signalsfrom said sensing means, and means for pumping a fluid into the inlet ofsaid microfluidic channel in response to commands from said analyzingmeans.
 6. The device of claim 1, wherein said sensing means comprises anoptical detector.
 7. The device of claim 1, wherein said opticaldetector is located in close proximity to said microfluidic channel. 8.The device of claim 7, wherein said optical detector comprises a lightsource located on one side of said channel and a light detector locatedon the other side of said channel such that the light from said sourcemay be altered by the presence or absence of a liquid in said channel.9. The device of claim 1, wherein said sensing means is capable ofdetecting wetout in said channel.
 10. The device of claim 1, whereinsaid sensing means is capable of detecting the presence of a liquidwithin said channel.
 11. The device of claim 1, wherein said sensingmeans is capable of detecting the presence of a gas within said channel.12. The device of claim 2, wherein said electrode assembly is locatedwithin said channel and is capable of detecting the flow speed of fluidsflowing within said channel.
 13. The device of claim 5, wherein saidpumping means is capable of changing the flow rate of a fluid withinsaid channel in response to a command from said analyzing means.
 14. Thedevice of claim 1, wherein said sensing means is capable of detecting ameniscus of a liquid flowing within said microfluidic channel.
 15. Thedevice of claim 1, wherein said sensing means comprises a hot wireanemometer.
 16. The device of claim 5, wherein said pumping means iscapable of stopping a fluid from flowing within said channel in responseto a signal from said analyzing means.
 17. The device of claim 5,wherein said analyzing means includes a computer link.
 18. The device ofclaim 1, wherein said fluidic properties include conductivity.
 19. Thedevice of claim 1, wherein said fluidic properties include capacity.